| With the rapid economic development of Jing-Jin-Ji region and the introduction of a series of measures for air pollution prevention and control,the type of air pollution in Beijing has gradually changed from coal smoke pollution in the 80-90 years of last century to the complex pollution at the beginning of this century.The particulate matter pollution is very serious in Beijing,especially for fine particulate matter(PM2.5).PM2.5 can not only reduce atmospheric visibility,have direct or indirect effect on environmental changes and global climate,but also profoundly influence human health.These effects are mainly dependent on the concentration level and chemical composition of PM2.5.Therefore,it is of great importance to study the chemical composition and source apportionment of PM2.5 in Beijing area.In order to understand the characteristics of chemical composition and sources of PM2.5 in typical aera of Beijing,three medium flow particulate matter samplers(TH150C Wuhan Tianhong)were used in the urban site(the meteorological tower super station of the Institute of Atmospheric Physics of the Academy of Sciences),the suburb site(the Xiangshan station of the Institute of plant research,CAS)and the urban background site(Huairou campus of the University of Chinese Academy of Sciences).Synchronous observation was carried out to obtain the sampling of PM2.5 fr-om 2014 to 2016.The concentration level,temporal and spatial distribution of PM2.5 chemical components(including water soluble inorganic ions,mineral and trace metal)were discussed.The characteristics of the spatial variation are analyzed,and the source apportionment of PM2.5 at three sites were also analyzed by using the receptor model.The main chemical composition of PM2.5 at the three sites are SIA(SO42-,NO3-and NH4+),organic matter(OM)and Mineral dust,the sum of which contributed approcimately 80%of PM2.5.The concentration of OM,EC,SIA and Trace metal in there three sites followed by:Urban>suburb>urban background area,while Mineral is highest in suburban,and then in urban and urban background area.The highest concentration of OM and EC was observed in winter,which the highest concentration of SO42-and NO3-were observed in summer and in autumn,respectively.In contrast,NH4+showed weak seasonal variation.Mineral dust was higher in spring and winter,and lower in summer and autumn.the highest value of trace metal was observed in winter.From clean days to heavy pollution days,the contribution of Mineral dust and trace metal are reduced,while the contribution of SI A increased rapidly from 37.4%,32.8%and 47.9%during clean days to 49.9%,47.77%and 53.3%during the heavy pollution period for the urban,suburb and urban background site,respectively.PMF model was used to resolve the sources of PM2.5 in this study,seven kinds of sources were resolved in the urban site,which including the secondary inorganic aerosol(45.6%),motor vehicles(22.7%),regional floating dust(12.5%),industrial source(6%),road dust(4.6%),coal combustion(4.2%),and biomass burning(3.7%).Six sources were resolved at the suburb site,including secondary inorganic aerosol(47.1%),motor vehicles(22%),regional floating dust(10.5%),road dust(9%),industrial source(6.2%),biomass and coal combustion(5.3%);And seven sources of PM2.5 were resolved for urban background site,including second inorganic aerosol(44.5%),motor vehicles(27.9%),road dust(8%),biomass and biomass combustion(7.3%),industrial source(6.8%),regional floating dust(2.8%)and heavy-oil combustion(2.7%).The main contributor of the evolution of haze pollution in urban and suburban sites is secondary inorganic aerosols,while there are secondary inorganic aerosols and motor vehicles emissions for urban background sites.In a word,seconday inorganic aerosol is the primary contributor to the formation of haze pollution in Beijing,and the motor vehicle emissions and the secondary formation of particls from gaseous pollutants further exacerbated air pollution during the heavy pollution period. |
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